Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing my new design.

The broken lines showing of the device are included for the purpose of illustrating environmental structure; the broken lines showing of the edge of the display screen and portions of the graphical user interface, including the text, are included for the purpose of illustrating portions of the article; all broken lines form no part of the claimed design. 

CLAIM The ornamental design of a display screen or portion thereof with a graphical user interface, as shown and described. 